In many electronic applications, it is often desirable or even required to protect electronic circuitry, such as on a printed circuit board (PCB), from unlawful or unauthorized access. This is especially true for electronic circuitry that includes cryptographic modules or functionality. For example, postage security devices (PSDs) are required by the United States Postal Service to comply with FIPS 140-2 level 3 issued by the National Institute of Standards and Technology (NIST). FIPS 140-2 level 3 requires that PSDs have a full envelope of physical tamper protection and detection which encloses all electrical nodes.
Prior art methods of tamper protection, such as disclosed in U.S. Pat. No. 5,858,500, involve wrapping the electronic circuitry, such as a PCB, in a flexible tamper respondent laminate. Such laminates are formed from a flexible film and typically further include circuit elements, such as traces made of conductive ink, used in detecting tamper attempts. Specifically, in the prior art, after first soldering the electrical connections to the PCB in place, the laminate is wrapped around the outer form of the PCB much like a gift box is wrapped in wrapping paper. Next, the wrapped PCB is typically inserted into an outer enclosure, such as an aluminum case, and potted using an encapsulating epoxy or the like. An example of a PCB wrapped in a tamper wrap according to such a method is shown in FIG. 1 at numeral 5. A significant problem with this method is that the corner edges 10 of the wrapped PCB 5 end up having a number of overlapping layers of the tamper wrap, referred to as mechanical stack up, due to the multiple folds that are required to wrap the PCB in its entirety. These overlapping layers are cumbersome to deal with during assembly procedures and result in an overuse and waste of tamper wrap material, which is typically expensive. Choosing not to cover such corner edges with the tamper wrap at all is not a viable solution to the problem of mechanical stack up since doing so would make the corner edges particularly vulnerable to attacks, such as through the introduction of a monitoring probe.